Refractometer



H. W. STRAAT REFRACTOMETER April 3, 1956 2 Sheets-Sheet l Filed Oct. 22, 1954 April 3, 1956 H. W. STRAAT REFRACTOMETER Filed Oct. 22, 1954 2 Sheets-Sheet 2 FIC 69\\ I+ 73754 1N E 64 85 V NToR HAROLD STRAAT BY ATT OBNEYS vFig. 1.

United States Patent vREERACTMETER Harold W.\Straat, iroztdequoit, N. Y., assigner to Bausch & Lomb kOptical Company, Rochester, Y., a corporation of New York Application ctober 22, 1954,' Serial No. 464,044

9-Claims. (Cl. SiS-14) This invention relates to refractcmeters of the Abbe type and more particularly it relates to improvements in the operating mechanisms therefor.

Conventional refractometers of kthe Abbe type have been constructed with the refracting prism andvftelescope pivoted relatively to each other. In some current models of the Abbe refractometer, the refracting prism and telescope axis are xed relative to each other on the housing and amirror is moved along the optical patlrbetween the prism and telescope for making settings of the instrument. Such types, although obviously improving upon the prior refractome'ters, have some disadvantages. For instance, the mirror in one of such types of instruments is mounted on a member which moves on an arcuate track about a center of curvature which is imaginary. This method of mounting and supporting the arcuate track and mirror is complex, making the instrument expensive to build and maintain.

In another Abbe type refractometer having the prism and telescope axis xed relative to each other, a mirror is pivotally mounted about a real center within the housing, but the drive means for the mirror mounting bracket is extremely costly and subject to inaccuracies.

It is, therefore, an object of thisinvention to overcome the above-noted disadvantages and to provide an improved refractometer of the type described having a fixed p ivot center for the moving mirror.

Another object of this invention is to provide a refractometer which can be used for determining the refractive indices of materials Athroughout a relatively wide range of indices.

A further object of this invention is to provide a refrac- A'tometer having an improved illumination system and optical system making it possible vto View through'the same eyepiece either the borderline of total reiiectionor the scale.

A still further object of this invention is to'provide a refractometer that is efficient and accurate in operation yet is economical to build and maintain.

And a still further object of this invention is to provide a refractometer that has the telescope eyepieceand ysample receiving surface of the prism facing the operator so as to facilitate loading the instrument.

These and other objects and advantages reside in certain novel features of construction, arrangement, and combination of parts as will hereinafter be more fully Adescribed and pointed out in the specification and appended claims.

Referring to the drawings: A

Fig. 1 is a vertical sectional view, with parts in` elevation, of a refractometer embodying the improvements of g the present invention.

Y Fig. 2 is a perspective view of certain details of the invention "Fig, 3 is a sectional View taken on the line 3,-.3 in

Y Fig. 4 isk a sectional view taken on the line in Fis.- 3-

44s by'a'partially retiecting, l f'splittertype'mirror 145; The beam splitterfi bends the ice 2 lFig. `5 is a partial front elevational view with parts broken away and in section.

Fig. 6 is` a -schematic diagram of the optical system and illuminating system of the instrument.

In the preferred form of the invention, as shown in the drawings, `the refractometer comprises a-housing 10 integrally formed with a base 11 and having an interior chamber 12 into which access is gained by removing screws 13 from the cover plate 14 on one side of said 'housing 10.

A front wall 15 on the housing 10 has an offset portion comprising a horizontal support 16 and a vertical wall 17 having an opening 18 .communicating with the chamber 12. Fitting into and attached tothe olset portion isan insert member having a base 19 and an'upstanding lwall Ztlwhich has `an opening `21 in alignment with-the opening 1S in the verticalrwall 17. Mounted on the base v19 is-a heat exchange unit 22 lwhich has a rear face 23 sloping downwardly andrearwardly thereof toward the Vprojection or rear portion 24 of the horizontal support 16 which extends slightly into the chamber 12. Mounted onV said heat exchange unit 22 is a refracting prism 25 having a rear face 26 sloping downwardly and forwardly. The lower rear edge of the prism 25 and the upper rear edge of the heat exchange unit 22 meet substantially along a common line so that the combined area of the rear faces of the heat exchange unit and prism is substantially coextensive with the area ofthe opening 21. l

The prism 25 Yhas a horizontal top surface 27 forreceiving samples under examination. A mating prism 28,' carried by a frame 29, ismounted to pivot aboutV a pin 30 onthe housing lil so that prism 28 may be swung out of contactwith the surface 2' in order that a liquid sample to be tested may be placed between the prism 28 and the surface 27 for holding the sample in the manner well known in the art. A second Aheat exchange unit 22 is formed in the frame 29 whereby a iluid having a carefully controlled temperature kmay be passed through the two 'fheat exchange units 22 for controlling the temperatures of ,the prisms andsample. y

A second opening 33'in said frontwall 15'has rotatably mounted therein a ring 34 marked with oppositely arranged twin compensator scales, which when 'read with respectto av reference point, indicate the angular position Vto the left or right of a pair of Amici prisms 35 mounted in the tube 36 attached'y to said ringl kfor achromatiza- `tion of the line of total reflectance in the field of view of the instrument. A transparent plastic cover plate 37 is snappedonto the housing 10 by means of clips 3,8 Afor coveririgtheV ring 3 4 tov protect against accidental turning of saidfringand-to form adust seal for the chamber ,12.

Projecting upwardly and forwardly from the klip of opening 39 in the forward wall 15 `is a sleeve @0in whichy is mounted an opticallsystem including a telescope 31 having anV eyepiece .42 aligned along an optical axis 43fbent at partially transmitting beam optical-axis ofjthetelescope so that a pair of conventional lens elements 46, mounted yin tube 36, together with the Amici prisms-35 complete the telescope system which will llie along an axisjincliued at an angle with respect to lthe v plane of the sample surface of the prism. The telescope eyepiece 42`is mounted on the same side ofthe instrument as the horizontal surface '27 of the lprism `25 'so' that an operatcnY ofthe instrument may load the'sample onto the prism 25 ovithoutreaehing around the instrtnnent. 'This isa .distinctraduantage .overprior art instruments in'which theprismis loeatedon the side opposite the operator, necessitating-awkward -reachingsaround the; instrument for P iyotedahour a-1nin-416 0.11 .housing 10 isos 4'/ which st .lpportsY a hubz48 having an otfset lip 4 9.for

centrically positioned clear plastic torio lens 51, both last-named elements enclosing a light source 52. Rota- .tion of the split ring 50 and toriclens 51v about their horizontal axis, as well as Ypivoting theyhub 48 about pin 46, will permit the adjustment .of the light source 52 in proper relationshipwith respect to the prism 25 for illuminating a sample under-examination.

Mounted within the chamber 12 in the housing 10 below and forwardly of the rear face portion 26 of the prism on a pivotpin 53 is a bracket 54 having in its upper edge a reentrant portion 55 which has spaced diverging walls 56, 57 upwardly extending from a dat tened web 58. Adjustably fastened by screws 59 in the reentrant portion 55 on the ilattenedweb 58 is a mirror 60 which is mounted on a cup-shaped element 6i in spaced relation to the diverging wall S6 and the pivot pin 53. Lying in substantially the saine piane with said pvot pin 53 is the mirror 68 which is mounted in posi- "tion to receive light rays fromV the prism 25 and direct them into the optical system so that all retracted rays from the prism will be directed along the optical axis of the telescope. The spacing between the mirror 60 and the diverging wall 56 of the bracket 54 is such as vtoV accommodate the rear portion 24 ofthe horizontal support 16 and the rear face 23 of heat exchange unit 22 throughout a substantial portion of the arc of movement of the bracket 54 and thereby permit a large arc of movement for the mirror 6i) relative to the prism A25. The pivot pin 53 is placed as far forward of the rear face 26 of the prism 25 as is mechanically possible to provide the maximum range of travel for the bracket 54 from one extreme position of the ymirror to the other.

With the plane of the mirror lying in substantially the same plane as the'pivot pin, any movementoflthe mirror about the pivot pin will be a true rotational movement and will not have translational or sliding motion. With this motion of the mirror all rays, including extreme rays, will be directed in the direction of; the telef.

scope and along the optical axis of the telescope. Y

The bracket 54, having an arcuate slot 62 through a portion 63 which is spaced from the pivot pin 53, has fastened over said arcuate slot 63 a translucent scale 64 which is calibrated in appropriate units. Fastened to and, in part, spaced from said portion 63 of thebracket 54 is an arcuately shaped track 65 lying substantially parallel to the arcuate slot 62 and having its center of curvature on the axis of the pin 53. A frame 66, attached to the housing 1t) by screws 67, has integrally formed therewith a sleeve 68 which supports an actuatt ing device 69 in position with respect to the track 65 so that turning said actuating device 69 will move the pbothrwith shoulder 78, and `with. the inner surface of bracket 54 about the pin 53 and will sweep the mirrorY through the rays retracted from the prism 25. j

Said actuating device 69, best shownjin Figs. 2 and 4, comprises a cylindrical bearing 70 vconcentrically mounted between the Vsleeve 68 Yand a rotatable` shaft 72`mounted on one end thereof for frictionally engaging one edge of the arcuately shaped track 65. Fastened on the other end of shaft 71 is a knob 74 which, when turned, is adapted to move the bracket 54 about the pivot pin 53. The knob end of shaft 71 is internally bored for rotatably receiving a rod 75 having a second knob 76 fastened thereon for interttng into a recessed portion of the knob 74. Said rod 75 has a narrow neck portion 77 which tapers outwardly into an enlarged shoulder 78. The bored portion of the shaft V71 has formed in a wall portion thereof a plurality of'holes 79 in which are seated a plurality of balls 80 which are spaced around the neck portion 77 of the rod 75. A' pair of balls 81, separated by a spring 82, are nested in a blind hol e 83 in the shaft 71 with one of said balls Slibearing against the end of said rod 75 for frictionally engaging the balls Said shaft 71 extends into the space Ybetween the` track 65 and bracket 54 and has a pair of friction-discs bearing 70. VRotation of the knob 74-will rotate the shaft 71 and friction discs 72 to move the bracket 54 about'pin 53 with a speed ratio of one to one. However, rotation of the knob 76 will rotate the balls 80'which'will in turn rotate the shaft 71 and discs 72 for moving the bracket 54 about pin 53 with a substantially reducedV ratio depending on the diameter of the balls 80, the diameter of the contacted portion of the enlarged shouldery 78 and the inside diameter of thev bearing 70. n `Thepreferred speed reduction ratio is five to onefor producing Y a reasonably ne adjustment for the instrument. Y'The friction drive arrangement for the new refractometer is a positive driving arrangement for moving the bracket and the mirror. `It is etcient in operation and cheap to build and maintainsince it requires no costly Vmachining or gear cutting operations.

The preferred form of a scale viewing opticalsystem, best shown in Figs. l and 6, `comprises a strip of clear plastic 85, made of Lucite, for example, having a light reflecting surface 86'so positioned in the housing that illumination from the light source V87 will be directed upon the scale 64. An image of the illuminated scale .is reliected by mirror 88 to condenser lens 89 and prism 90 where it is transmitted through the beam sp1itter45 to the eyepiece 42 of the telescope 41. Angularly formed on one end of a plug 91 is the mirror 88 which is maintained atan angleof approximately 45 to the horizontal. The other end of the plug 91 has'a slotted head 92 which is used to rotatesaid plugV 91 andmirror 1 l 88 for adjusting the angle of the mirror 88 relative to the" n optical axis of the beam of light from source 87 to the eyepiece 42. It is desirable thatthe longitudinal axis of the plug 91`lie in theplane of and parallel to the ilongitudinal axis of the pivot pin 53 of the bracket .54.

.Wherefore when the plane of the mirror 88 and the plane of the optical axis of the source 87, strip and, lensY 89 lie perpendicular to each other, the largest viewing apertureV of the scale64will berpresentedto the telescope system. Slightv deviation from the just-described condition will change the shape of the aperture from round to oblong thus cutting down the size -of eld viewed. Y

The light sources 52 and 87 are connected to opposite sidesvof a switch 93 in such a way that either one or the The lead 94 is connected to the switch 93 and to an appropriate source other source may be energized at one time.

of electricity. ,n v

The lens 89 and prism 90 are mounted in artube V95 which is adjustably fastened to the housing 10 by means ofa bracket 96 and screw 97 as well as by means of adjusting screw 98 on the arm of the frame 66. A combination of adjustments of screws 97, 98 will accurately adjust theY scaleyiewing portion of the secondV optical A system. Y Y Y The beam splitter 45 is composed of a glass plate that has a coatingthereon which partially transmits and par-` tially rellects Ylight rays so that when light source'52 is Y,

. energized, an observer looking Vintoeyepiece 42 may, v. Y

after adjustment of the bracket 54 and mirror 60view the borderline of total `reflection of the sample being examined since the beam splitter 45 will reflect to the eyepiece 42a substantial portion of the rays striking it from the mirrork 60. However, when light `source 87is Y Y energized, vthe light rays Yfrom the aligned portion'ofY scale 64 will beA transmitted through the beam splitter 45 for viewing in the eyepiece 42.

In operation, a drop of a sample Yto be tested is placed on the surface 27 of the prism 25 and the mating prism Z8 is closed onA top thereof. The light source 52 is energized and adjustably positioned relative to the prisms 25,

f 28 to provide the best illumination for the sample.A vBy turning knob 74 the bracket 54 and mirror60 will be pivoted about the pin 53 untila borderlineof totalrej ilection is viewed in eyepiece 42. The tine adjustment AJH..

knob 76 is then turned to set the borderlineof total I reilection in the correct position.. The'Amici prisms vvare adjusted, either before or after tine adjustment, for achromatization of the line of total reflection. .Once the borderline has been correctly positioned, the -light switch 93 is flipped to deenergize source 52 and lto energize source 87. In this way the borderline scale reading 64 may be viewed in the eyepiece to give the refractive index of the sample. If desired, the scale may be calibrated to give readings in terms of Percentage of Solids, Butyro numbers or any other units which are a function of refractive index.

From the foregoing, it will be obvious that there Vis Yhere provided a rugged, precision refractometer having a wide and complete range of refractive index readings.

Effective means are provided for improving the illumination and optical systems making it possible to view both the borderline of total reflection and the scale reading in the same eyepiece. An instrument is provided that is eiicient and accurate in operation yet is economical vto build and maintain. Although but lone form of this refractometer has been shown and described in detail, it will be understood that other forms are possible and changes may be made in the arrangement and detailed structure of the parts and substitutions may be made without departing from the spirit of the invention asdetined in the claims here appended.

I claim:

1. In a refractometer the combination of a housing having a front wall provided with an opening, a horizontal support carried by the front wall and having a projection vextending into the housing adjacent the opening, `a refracting prism carried by the support, an opticalpsystem including a telescope carried by the Ahousing kabove the plane of the prism, a bracket mounted to turn about a pivot pin which is carried by the housing below andforwardly of said projection on said support, means for moving said bracket, a mirror carried by thebracket in position to receive light rays from the prism and `'direct them into the optical system, said mirror and fpivo't pin lying in substantially the same plane, the portion of the bracket lying between the pivot pin andthe mirror being formed to provide a space into which the projectionwis received when the bracket is moved upwardly whereby the operating range of the instrument is increasedf" 2. A refractometer comprising a housing4 having a front wall with an opening therethrough, a horizontal support carried by said front wall below said opening and having a projection extending into the housing, a refracting prism carried by said support, a light .source movably mounted on the front wall of the -hou-sing in spaced relation to a sample receiving surface of the prism, a bracket mounted to turn in the housing abolita pivot pin carried by the housing below and forwardly of the projection on the support, a mirror carried by said bracket and lying substantially in a plane containing the axis of the pivot pin, the portion of the bracket between the mirror and pivot pin being formed to provide a space into which the projection of the support is received when the bracket is moved upwardly, means for turning the bracket about the pivot pin, an optical system including a telescope having an eyepiece carried by the upper portion of the front wall of the housing and spaced above the prism and means carried by the housing in the optical path of the optical system for reiiecting the refracted rays from the prism and mirror to the eyepiece of the telescope whereby the borderline of total reilection may be viewed in the eyepiece of the telescope.

3. In a refractometer the combination of a housing, a horizontal support carried by the front wall of the housing and having a projection extending into an opening in the housing, a refracting prism carried by said support and having a rear portion facing said opening in the housing, an optical system including a telescope carried bY..-Said 1iosiss @entsinneuniversity@ an .anglewtth renten -t la hafisatel gustas@ f 11.1.@ Prises' a bracket .mounted toturn about `apivotpin carried byithe housing below land `forwardly of the projection of ythe support, said bracket having in `its ,upper V edge a :reentrant portion formed with spaced divergitig walls, a mirror carried .by said bracket in said reentrant portion ,in spaced relation with said ,walls to .provide an ,open space in the bracket between said mirror and said pivot pin, `said open space being yformed to .receiver `the .rear `portion of the support when the bracket is moved JJPWard-ly, said mirror and pivot pin lying insubstantially the saine plane for positioning the mirror to .receive -light rays from the prism and direct them into the Loptical system, and means for moving said bracket ,about said pivot pin whereby` `the mirror passes .through a lwide range .of retracted rays from the prism.

4. In a refractometer the ,combination of a housing having ya front wall .provided .with an opening therein, .a horizontal .support on ,the housing having. a projection .extending into said opening, `a refracting prism carried by. said support andhaving. a rear portion facing said opening, an .optical `system'including va-telescope xed on V`said housing, alight source vcarried by the housing in alignment with the prism. for-illuminating a .sample on ,saitl prism, a Ybracket havingone `end portion rpivotally mounted within the housingbelowand'forwardly of the rear. portion of ,theprisrm said bracket having in its upper edge a Vreentrant :portion formed .with .spaced diverging walls, a mirror carried by-said reentrant portion of the bracket in spaced relation .with the wallsof said reentrant portion, the projection of the support .being received in `the space betweenthefonwardi w'all ofthe reentrant por tion ofzthe bracket .andV the mirror 4.throughouta substantial portion of the arc of movementofthe bracket, said mirror being positioned `to receive light rays from the light source land prism and .direct them into lthe optical `system throughout `the full 4range of movementl of the bracket, .scale meansonhe opposite end portion vof said bracket, a secondlightsource in they housing for illuminating said scale means, opticalmeans for transmitting the scale reading to thetelescope, switch means foralternatively energizing vthe light` sources, and drive means` engaging with the bracketfor moving1said `bracket and mirror whereby the borderline ptotal reflection and its concomitant scalereadiug maybe viewed in the telescope by alternatively `energizing the. respective `light sources.

5. In a refractometerhaving a vhousing with a front wall, an `offset portion in said front wall comprising a .vertical wall having an opening therein and va horizontal ,supportv extending into said opening, a refracting` prism ,carried by said support, and au optical system including a ltelescope carried by saidghousingandhaving its Yoptical axis fixed relative to said prism, the combination of a movable mirror mounted adjacent the rear portion of said prism and the optical axis of said telescope for reflecting light rays from the prism along the optical axis of the telescope, means for pivotally mounting said mirror on said housing comprising a bracket having a reentrant portion in the upper side, a pivottpin passing through one end of said bracket for pivotally mounting said bracket to said housing below and forwardly of the rear portion of said support, said mirror being mounted in and to one side of said reentrant portion in said bracket for providing an opening between the mirror and the pivoted end of the bracket, the horizontal support for the prism fitting into said opening between the mirror and bracket throughout a substantial portion of the arc of travel of said bracket about the pivot pin, scale means on the bracket spaced from the pivot pin, optical means for forming an image of the scale in the telescope, and

drive means for moving said bracket about said pivot pin for sweeping the mirror and scale through the range of refracted rays of the prism.

6. A refractometer comprising a housing having a 'front wall with an opening therethrough, a horizontal sup- Y port carried by said front Wall and having a projection extendingV into' the housing adjacent the opening, a` refracting prism carried by said support and having a rear portion facing'said opening in the housing, an optical systemV including a telescope having an eyepiece carried by the housing above the plane of the prism, a light source carried by the housing for illuminating a sample receiving surface of the prism, a bracket mounted to turn about apivot pin which is carried by the housing below and forwardly of the projection on thesupport, a mirror carried by said bracket and lying substantially in a plane of the pivot pin, said mirror being positioned to receive light rays from the prism and direct them into said ^op tical system, said bracket having a portion lying between the pivot pin and mirror formed to provide a space into which the projection of the support is received when the bracket is moved upwardly, means for moving said bracket about said pivot pin, a scale carried by a portion of the .bracket spaced from the pivot pin, a light reiiecting and light transmitting beam splitting mirror carried by the housing along theaxis of the optical system for reecting the light rays from the prism to the eyepiece, a second optical system in optical alignment with the beam splitting mirror for transmitting light rays from the scale to the above-named eyepiece, asecond light source carried by the housing for illuminating the scale for the second optical system, switch means for selectively energizing the first and secondl light sources whereby light rays from the prism and their. concomitant scale reading may-bel selectively viewed inthe eyepiece.

7. In a refractometer the combination of a housing having a front wall with an opening therein, a horizontal support carried by "said front wall and having a projection extending into said opening, a heat exchange unit mounted on said support, a refracting prism mounted on said heat exchange unit and having a rear portion facing Y said opening, said heat exchange unit controlling the tcmperature of the prism, an opticalrsystem carried by the housing and having a telescope carried by the front wall in a plane above the plane of the prism, a bracket mounted to turn about a pivot pin which is carried by the housing below and forwardly of the projection on the support, a mirror carried by the bracket and lying in substantially the same plane as the pivot pin, said mirror being positioned on the bracket to receive light rays from the prism and direct them into the optical system, said bracket having a portion'lying between'the mirror and pivot pin formed to provide a spaceV into which the projection of the support is received when the bracket is moved upwardly, means for turning the bracket about the pivot pin, and scale means carried by the bracket and coordinated with the position of the mirror in the path of adjustments to said shaft.,

y 8 t t light rays whereby for each s etting'of the mirror there is a `corresponding scale reading.'V i

-8. In a refractometer havingY aV housing, a refracting prism and an optical system carried by the housing at an angle relative vto each other, and "a mirror movably mounted in the housing for reecting light rays from` the prism into the optical system,4 the combination of means for movably mounting said mirror in said housing comprising a bracket, a pivot pin carried by the housing and passing through Voneend portion of the bracket for pivotally mounting the'bracket inthe housing, a scale carried by the bracket, means cooperating with the scale for indicating themovement of the mirror in terms of re fractive index, an arcuately shaped track carried by and spaced fromthe'bracket, the arcuate portion of the track having its center of curvature substantially at said pivot pin, a rotatable shaft carried by the housing and extending into the space between the'bracket and thetrack, a

pair of friction'discs fastened'to said shaft and engaging with said trackfand means carried by the Vvshaft and housing for providing coarse and line adjustments for said shaft whereby-turning theshaft will move the mirror through the path of light rays.

9. A refractometer comprisingl a housing having a front Wall, .a refracting prism carriedby` said front wall, an. optical system includingfa telescope carried by the housing above the plane of the prism, a bracket in the housing mounted to turn about a pivot pin, a mirror carried by the bracket and positioned to receive'light rays tromthe prism` and direct them into said optical system, said bracket having an arcuate slotQ therethrough which is spaced from'the pivot pin, a translucent scale' mounted "over said slot in alignmentwith'a light source for illumiarcuate portion of the track lying substantially parallel to the'arcuate slot in the bracket, means for turning said bracket about said pivot pin Vcornprisinga rotatable shaft carried by the housing and extending into the space bei tween the bracket and the track, a pair of friction discs fastened to said shaft andrengaging With said track,'and

means carried by the shaft for providing coarse and tine References Cited in theile of; this patent FOREIGN YintrantsY 257,127 Great Britain ug. 26, 1926 462,332 Great Britain Mar. 8, 1937 690,268 Greatnrifam ---l Apr.'15,'1953 

